This project will concentrate on the characterization of unbroken chromosomal DNA from bacteria and higher organisms. Extensive use will be made of the measurements of the viscoelastic properties of dilute solutions, a technique recently developed in this laboratory, and one that is especially suitable for characterizing very large DNA molecules with respect to size. These measurements can be carried out on impure lysis mixtures, but a search will also be made for methods of purifying the DNA without breaking the exceedingly fragile molecules. Studies on the mechanism of mechanical breakage of DNA will be continued to attempt to define the effect of molecular weight, and to compare double with single strands. Measurements of the molecular weight of the primary molecules in lysates will be used to attempt to determine the strandedness of the original chromosomes from various tissues in various organisms. The effect of very low doses of radiation and mutagenic agents on DNA molecular weight will be examined. Refinement of the viscoelasticity apparatus itself will be carried out to improve accuracy and ability to resolve complex mixtures. The theory of sedimentation anomalies encountered with very large DNA molecules will be extended.